Editing SM-65 Atlas (section)

==='Stage-and-a-half'===
Atlas was informally classified as a "stage-and-a-half" rocket, with a central sustainer engine and set of two booster engines that were all started at launch, each drawing from a single set of propellant tanks.<ref name="Brugge">{{cite web |url=http://www.b14643.de/Spacerockets/Specials/Atlas_MA-drive-system/index.htm |title=Variants of the "stage and a half" drive system (MA) of the Atlas rocket |website=b14643.de |access-date=4 September 2022}}</ref><ref name="McCutcheon">{{Cite web |last1=D. McCutcheon |first1=Kimble |title=Part 5: The Atlas Missile |url=https://www.enginehistory.org/Rockets/RPE05/RPE05.shtml |url-status=live |archive-url=https://web.archive.org/web/20240828191532/https://enginehistory.org/Rockets/RPE05/RPE05.shtml |archive-date=28 August 2024 |access-date=4 September 2022 |website=U.S. Manned Rocket Propulsion Evolution }}</ref> Most [[multistage rocket]]s drop both engines and fuel tanks simultaneously before firing the next stage's engines. However, when the Atlas missile was being developed, there was doubt as to whether a rocket engine could be air-started. Therefore, the decision was made to ignite all of the Atlas' engines at launch; the booster engines would be discarded, while the sustainer continued to burn.<ref name="Brugge"/> A stage of a liquid propellant rocket normally consists of both propellant tanks and engines, so jettisoning one or more engines only is equivalent to "half a stage". At staging, the booster engines would be shut off and a series of mechanical and hydraulic mechanisms would close the plumbing lines to them. The booster section would then be released by a series of hydraulic clamps (aside from the early test model Atlas B, which used explosive bolts) and slide off the missile on two tracks. From there on, the sustainer and [[Vernier thruster|verniers]] would operate by themselves. Booster staging took place at roughly two minutes into launch, although the exact timing could vary considerably depending on the model of Atlas as well as the particular mission being flown. This "stage-and-a-half" design was made possible by the extremely light weight [[balloon tank]]s.<ref name="McCutcheon"/> The tanks made up such a small percentage of the total booster weight that the mass penalty of lifting them to orbit was less than the technical and mass penalty required to throw half of them away mid-flight. However, technology advanced quickly and not long after design work on Atlas was completed, Convair rival Martin proposed a solution to the air-starting problem. Their [[Titan I]] missile, developed as an Atlas backup, had a conventional two stage design.<ref>{{cite web|title=The Military Standard - Titan I Missile Overview |url=http://www.themilitarystandard.com/missile/titan1/overview.php|website=themilitarystandard.com|access-date=March 10, 2023}}</ref>